1. Field of the Invention
This invention relates to apparatus for separating a pressure plate from the extrusion residue in the extrusion of metal with a shell
2. Description of the Prior Art
To ensure that impurities on the surface of a billet to be deformed by extrusion do not enter the extrusion product, extrusion may be performed with a shell, particularly when raw heavy metal billets (copper or brass) are used. The pressure plate is then kept smaller in diameter than the internal diameter of the billet receiver, so that a shell approximately 0.5 to 2 mm in wall thickness remains at the bore wall in the billet receiver.
The shell is removed by means of a stripping or ejector plate, or cleaning plate, of the same diameter as the receiver bore. This can be a stripping plate connected to the pressure plate used for extrusion, with an integral neck between the pressure plate and stripping plate which leaves an empty annular chamber with space for the shell, which forms a crumpled ruff; alternatively, the ejector plate can be loaded after extrusion of a billet, and the shell can be compacted and ejected by the extrusion ram in a further ram stroke. The pressure plate must then be freed of the extrusion residue, which cmprises the shell in the vicinity of the pressure plate, the remaining shell compacted into a ruff around the neck of the pressure plate or in front of the pressure plate, and, in direct extrusion, the unextruded billet residue, whereas in indirect extrusion the unextruded billet residue is separated along the die end face while still in the press to separate the extrusion product ("Fachberichte" 18 (1980), vol. 10, pp. 951/958, and "Metall" 31 (1977), vol. 2, pp. 151/156) which corresponds to English translation "Indirect extrusion of aluminium and copper rich tubes" by F. J. Zilges, Reprint from METALLURGIA (1981) No. 5, pp. 219/228.
German Patent Specification OS Nos. 25 06 447, corresponding to U.S. Pat. No. 4,048,832 and 26 13 241 describe apparatus for separating a pressure plate from the extrusion residue in direct or indirect extrusion of metal with a shell, that is, a "pressure plate separate", more particularly one which comprises a frame, a slideway running perpendicularly up to the frame, a pusher pushing the pressure plate through the frame opening, and stripping cutters provided at the sides of the frame opening. The stripping cutters at the sides of the frame opening are so formed and spaced that they touch the pressure plates on diametrically opposite generatrices while the plates are pushed along the slideway through the frame by the pushers. The cutters are intended thus to slit open the shell or compacted shell along the two diametrically opposite generatrices, so that the remaining shell halves can be released and removed. If, as usually occurs in direct extrusion, the shell is connected to a billet residue, the frame is provided not only with the stripping cutters, but with one or two cutters above and/or below the frame opening, to cut along the pressure plate end face or faces covered by the billet residue and possibly by the compacted shell (German Patent No. 1452462, corresponding to U.S. Pat. No. 3,373,592 and German Patent Specification OS No. 25 05 160, corresponding to U.S. Pat. No. 4,043,163). Known pressure plate separates do not offer the operational reliability needed for the desired automation of the process of separating the pressure plate from the extrusion residue. Adhesion of the extrusion residue to the pressure plate or slight bonding of material in the vicinity of radii at the edges of the pressure plate occasionally interfere with satisfactory separation of the pressure plate from the extrusion residue, so that manual intervention is required.